Composite veneers becoming yellow after a few days of having them replaced

I recently had my 10year old composite veneers removed. I had my teeth whitening using Zoom to give a cleaner finish. After a few days of the procedure I found my zoom whitening has disappeared and also my composite veneers look very cloudy/translucent/yellow. I do not smoke/drink/nor drink coffee. Why have my composite veneers changed so dramatically and look so yellow, has the dentist missed something? Should they have been finished off with a coat to seal/protect from stains? Please help.